For producing alcohols including aliphatic, alicyclic or aromatic alcohols by hydrogenation of carboxylic acids or carboxylates, there have been many methods disclosed from the 1930s onward. In hydrogenation of carboxylates, particularly of fatty acid esters, use of copper-based catalysts has been mainly proposed.
Conditions for reductive activation of these catalysts are determined according to a form in use, a method of use, a mode of reaction, and the like. For example, in a fixed-bed reaction system, a molded catalyst is entirely subjected to gas phase reduction for activation. In industry, such reduction of a catalyst is generally carefully conducted at a predetermined temperature under an inert gas flow that contains several to several tens percent of hydrogen in order to avoid local overheat due to rapid reduction of the catalyst. For instance, JP-A 61-161146 describes disadvantage of such gas phase reductive activation of a catalyst concerned with productivity of an alcohol as taking a time from 4 to 14 days.
As described above, fixed-bed reaction systems generally employ gas phase reduction, but some systems employ liquid phase reduction to activate a copper-containing catalyst precursor. For example, JP-B 2990568 discloses liquid phase reduction of a molded precursor of a copper-containing hydrogenation catalyst, that reduction is conducted at a temperature ranging from 50 to 140° C. According to this method, a copper-containing hydrogenation catalyst can be prepared that has significantly improved catalytic activity and selectivity compared with that prepared by gas phase reduction. However, in Examples and Comparative Examples of JP-B 2990568, a catalyst prepared in Example 1 in which reduction is conducted at 130° C. and a catalyst in Comparative Example 2 in which reduction is conducted at 200° C. are almost similar to each other in selectivity. Comparative Example 2, however, has a high catalytic activity by about 10% than Example 1. The reason of necessity of the upper limit of a reduction temperature in spite of an increased catalytic activity by reduction at higher temperature is as follows. As described in paragraphs 0010 and 0011 of JP-B 2990568, liquid phase reduction conducted at too high temperature will deactivate a catalyst with water and fatty acid, and will largely decrease a purity of a solvent with ester wax and hydrocarbons, that by-products are generated during a reduction treatment.
In order to increase catalytic activity and selectivity, JP-B 3195357 discloses a two-step reduction of a molded precursor of a copper-containing hydrogenation catalyst, including a first step of reducing the precursor in a liquid phase at 20 to 140° C. such that at least 10% by weight of copper oxide is reduced at a point of reaching to 140° C. and then a second step of further reducing the precursor in a liquid phase at 140 to 250° C. As described in Examples and Comparative Examples of JP-B 3195357, catalysts prepared in Examples had relative activities 1.2 to 1.5 times higher than that of a catalyst prepared by gas phase reduction in Comparative Example 1, which clearly shows an advantage of the disclosed liquid phase reduction. However, in any of these Examples and Comparative Examples, a reduction temperature was finally increased to 170 to 200° C., suggesting decrease of purity of a solvent.